This section of the Aspen Trail heads from the Marshall Gulch Picnic Area up to Marshall Saddle. It begins to the left (south) of the bathrooms as a singletrack leading sharply up the hillside. The beginning section of this trail is particularly challenging before flattening out a bit on the middle and upper sections. It's definitely a longer and more challenging route up to Marshall Saddle than the alternate Marshall Gulch Trail #3. The primary difference being that there are much steeper sections of trail here, while the Marshall Gulch Trail is a more constant climb. It is a bit less traveled, although it's still likely you'll encounter other trail users on the weekends.
The early sections of this trail tend to have more large bushes adding some humidity at times, before giving way to slightly more open treed sections, with intermittent bushy areas. The trail isn't all that technical, but has its moments of rocky sections. Using this route and the Marshall Gulch Trail #3 makes for a nice loop in and out of the Marshall Gulch Picnic Area.